Pumps are used in a wide variety of applications to transport various types of materials. Centrifugal pumps, for example, are typically used to transport fluids. Such pumps are adapted for use with a motor having a rotating motor shaft, and generally include a housing defining a pump chamber, a fluid inlet, a discharge outlet, and a shaft opening. An impeller shaft is attached to the motor shaft, extends through the shaft opening in the pump housing, and has an end disposed inside the pump chamber. An impeller is attached to the impeller shaft so that, as the impeller rotates, fluid is drawn through the inlet and discharged through the outlet.
Such pumps typically include a seal at the shaft opening in the pump housing to prevent fluid from leaking along the impeller shaft. Such seals are typically provided in the form of a gasket, such as an o-ring, which is attached to the shaft opening and engages the impeller shaft. Conventional gasket seals, however, create a number of problems. Not only do the gasket seals themselves wear out, but the seals also cause wear on the impeller shafts. Such seals do not tolerate a shaft which rotates with a wobble or some other type of eccentricity, and the seals generate heat due to friction between the stationary seal and rotating impeller shaft. In addition, gasket seals rapidly wear out and fail when the pump is operated dry (i.e., when pump chamber is not filled with fluid). Furthermore, all gasket seals leak to some extent, regardless of seal material or tightness.
In one application, a centrifugal pump is incorporated into a vacuum cleaner. Tank-type vacuum cleaners have an air impeller disposed inside a tank which is capable of vacuuming dry materials such as debris or dirt and suctioning liquids into the tank. When the tank is full, the pump removes liquid from a lower portion of the tank and expels it through a hose to waste. As taught in commonly owned U.S. patent application Ser. No. 09/281,671 now U.S. Pat. No. 6,191,304, the air and pump impellers are advantageously connected to a common shaft which is rotating by a single motor. The air and pump impellers are mounted proximate one another in an upper portion of the tank, near the motor. As a result, it is important to prevent fluid from leaking through the shaft opening and into the air impeller and motor. It is also desirable, however, to use the vacuum produced by the air impeller to prime the pump.
In the above-referenced vacuum cleaner, a liquid deflector is positioned between the pump and air impeller to prevent fluid from reaching the air impeller and motor. In addition, the distance between the pump and the air impeller is increased, thereby lengthening the shaft. As a result, while these modifications adequately prevent fluid from reaching the air impeller and motor, the vacuum cleaner requires additional components, making assembly more difficult and expensive. Furthermore, the longer impeller shaft increases the likelihood of vibration and thus noise and additional wear on the shaft support bearings.
To utilize the vacuum produced by the air impeller to prime the pump, the impeller shaft is formed with a bore leading to an impeller backing plate formed with spacers, so that a path is formed from the air impeller, through the shaft, and to the pump chamber. A vacuum director is attached to the impeller shaft to further ensure that the vacuum is communicated to the shaft and ultimately to the pump chamber. Accordingly, the components used in the above vacuum cleaner are overly intricate and complex to assemble, and the weight supported by the rotating impeller shaft is overly excessive.